Add [W3C] Markup Validation Service Badge (#3833) (#4148)

* Add W3C Markup Validation Service Badge (#3833)

* Move helper functions into different file and added unit tests

* Remove unnecessary comments from spec file

* pr changes move code into transform method and validation of messages

* use joi.string().regex instead of custom validator

* Simplify the fetch, handle methods. Make Joi validation for string

* Remove empty parameter from tests and label from render method

* encodeUri on the doc and schema properties send to API

* Documentation and remove unnecessary Object.keys call

* Use regular expressions to make tests less brittle

* made service less for message and color more generic and less brittle

* Throw standard NoFound exception for invalid URL. Use w3c endpoint

* use sazerac for w3c-validation-helper.spec.js

* Replace documentation API url and API documentation url

* Switch back to https://validator.nu endpoint. Remove html4 assertions

* Increase strictness of NotFound checks